Republican presidential hopeful Sen. Marco Rubio on Monday made one of his most forceful calls yet for states to convene an Article V convention to amend the constitution, which as become key to his courtship of tea party voters.

The Florida senator beseeched voters to press their state legislatures for a convention of states, saying it was one of the only ways to rein in Washington and solve the looming debt crisis.

“As president, I can promote such a convention, but I cannot make it happen without the American people. That’s why I’m asking for your help today,” he said at a town hall-style meeting in Sarasota, Florida. “To any American worried about the debt we’re leaving our children: Join me in this effort. Press your state representatives to convene a convention of states.”

An Article V convention allows state legislatures to circumvent Congress and initiate a process to amend the constitution. It has become a popular cause among conservatives fed up with inaction from Washington on a host of issues, including seeking amendments for a balanced budget and further limiting federal power over states.

For states to call the convention, it would require approval from 34 legislatures. Over the past four decades, 27 states have endorsed the idea at one time or another. Convention proposals were also introduced or discussed in about three dozen legislatures last year.

The Convention of States Project has been spearheading the effort and has enlisted nearly a million volunteers and supporters covering all 50 states, according to the group’s website.

Mr. Rubio is the only major candidate to aggressively promote a constitutional convention, as he seeks to attract more tea party and conservative voters. In most polls, he is running third behind billionaire businessman Donald Trump and Sen. Ted Cruz of Texas, who are viewed as more conservative and anti-establishment than Mr. Rubio.

Mr. Trump has advocated changing the constitution but has not made the convention of states a rallying cry. Mr. Cruz has said that he supports the idea but that he is running for president to put the country back on track.

Other GOP contenders, including Ohio Gov. John Kasich, former Arkansas Gov. Mike Huckabee, Sen. Rand Paul of Kentucky and retired neurosurgeon Ben Carson have expressed varying degrees of interest or support for the Article V effort.

In the speech, Mr. Rubio bemoaned that most young voters believe the American dream is dead and the looming debt crisis. He also warned that Democratic front-runner Hillary Clinton’s high-tax, big-government policies would hasten the decline.

“Here’s what Barack Obama and Hillary Clinton don’t understand about free enterprise: In a free enterprise system, the president does not run the economy. The president’s job is to ensure policies are in place that allow the private sector to succeed, because it is the private sector that creates jobs and opportunity,” he said.

“As president, I will put Washington in its place. It will once again stand behind our people, not in their way,” he said.

He continued: “I will repeal and replace Obamacare before it repeals and replaces any more American jobs. I will shred Obama’s job-killing executive orders. I will cap the amount regulations can cost our economy. And I will end Washington’s addiction to wasteful spending. Because by the time our next president takes office, America will already be $20 trillion in debt.”